Shane A. O'Neill

Characterisation of the photocatalyst Pilkington Activ (TM): a reference film photocatalyst?

Pilkington Glass Activ™ represents a possible suitable successor to P25 TiO2, especially as a benchmark photocatalyst film for comparing other photocatalyst or PSH self-cleaning films. Activ™ is a glass product with a clear, colourless, effectively invisible, photocatalytic coating of titania that also exhibits PSH. Although not as active as a film of P25 TiO2, Activ™ vastly superior mechanical stability, very reproducible activity and widespread commercial availability makes it highly attractive as a reference photocatalytic film. The photocatalytic and photo-induced superhydrophilitic (PSH) properties of Activ™ are studied in some detail and the results reported. Thus, the kinetics of stearic acid destruction (a 104 electron process) are zero order over the stearic acid range 4-129 monolayers and exhibit formal quantum efficiencies (FQE) of 0.7×10−5 and 10.2×10−5 molecules per photon when irradiated with light of 365±20 and 254 nm, respectively; the latter appears also to be the quantum yield for Activ™ at 254 nm. The kinetics of stearic acid destruction exhibit Langmuir-Hinshelwood-like saturation type kinetics as a function of oxygen partial pressure, with no destruction occurring in the absence of oxygen and the rate of destruction appearing the same in air and oxygen atmospheres. Further kinetic work revealed a Langmuir adsorption type constant for oxygen of 0.45±0.16 kPa−1 and an activation energy of 19±1 kJ mol−1. A study of the PSH properties of Activ™ reveals a high water contact angle (67°) before ultra-bandgap irradiation reduced to 0° after prolonged irradiation. The kinetics of PSH are similar to those reported by others for sol-gel films using a low level of UV light. The kinetics of contact angle recovery in the dark appear monophasic and different to the biphasic kinetics reported recently by others for sol-gel films [J. Phys. Chem. B 107 (2003) 1028]. Overall, Activ™ appears a very suitable reference material for semiconductor film photocatalysis.

Titania and tungsten doped titania thin films on glass; active photocatalysts

Acidification of an isopropanol solution containing mixtures of [Ti(OPri)(4)] and [W(OEt)(5)] produced solutions from which various TiO2, WO3 and TiO2/WO3 thin films could be obtained by dip coating and annealing. The films were analysed by X-ray diffraction, SEM/EDAX, Raman, electronic spectra, contact angle and photoactivity with respect to destruction of an over layer of stearic acid. The TiO2/WO3 films were shown to be mixtures of two phases TiO2 and WO3 rather than a solid solution TixWyO2. The 2% tungsten oxide doped titania films were shown to be the most effective photocatalysts. All of the TiO2 and TiO2/WO3 films showed light induced superhydrophillicity.

Atmospheric pressure chemical vapour deposition of titanium dioxide coatings on glass

Atmospheric pressure chemical vapour deposition of titanium dioxide coatings on glass substrates was achieved by the reaction of TiCl4 and a co-oxygen source (MeOH, EtOH, iPrOH or H2O) at 500–650 °C. The coatings show excellent uniformity, surface coverage and adherence. Growth rates were of the order of 0.3 µm min−1 at 500 °C. All films are crystalline and single phase with XRD showing the anatase TiO2 diffraction pattern; a = 3.78(1), c = 9.51(1) A. Optically, the films show minimal reflectivity from 300–1600 nm and 50–80% total transmission from 300–800 nm. Contact angles are in the range 20–40° for as-prepared films and 1–10° after 30 min irradiation at 254 nm. All of the films show significant photocatalyic activity as regards the destruction of an overlayer of stearic acid.

The dual source APCVD of titanium nitride thin films from reaction of hexamethyldisilazane and titanium tetrachloride

Atmospheric pressure chemical vapour deposition reaction of TiCl4 and NH(SiMe3)2 at 300–550 °C produced films of titanium nitride on glass substrates. The films were gold or purple/gold in colour, highly reflective in the infrared but with significant transmittance in the visible. Growth rates were typically 300 nm min−1 at 550 °C. The films were uniform, adhesive, abrasive resistant, conformal and hard, being resistant to scratching with a steel scalpel. They also showed no change in optical properties on immersion in common solvents or dilute acids or alkalis (2 M). X-Ray diffraction showed preferred growth in the (2 0 0) direction, typical cell constants of 4.23(1) A and a crystallite size of ca. 200 A. Raman spectra matched powder samples. SEM indicated the films were composed of ca. 200 nm particles. EDAX and electron probe studies showed no carbon or silicon impurities and a titanium to nitrogen ratio corresponding to TiN0.95. X-Ray photoelectron spectroscopy gave binding energy shifts for Ti2p3/2 and N1s at 455.8 and 396.9 eV respectively. The sheet resistance of the films showed increase conductivity with deposition temperature. The titanium nitride films showed potential for heat mirror applications.

Tin phosphide coatings from the atmospheric pressure chemical vapour deposition of SnX4 (X=Cl or Br) and PRxH3−x (R=Cychex or phenyl)

Atmospheric pressure chemical vapour deposition (APCVD) of tin phosphide thin films was achieved on glass substrates from the reaction of SnCl4 or SnBr4 with R-N PH3-N (R = Cyc(hex) or phenyl) Lit 500-600 degreesC. These coatings show good uniformity and surface coverage. They are reasonably adherent, passing the scotch tape test. The films were largely opaque in appearance with regions of birefringence. The films were X-ray amorphous. Scanning electron microscopy (SEM) showed surface morphologies consistent with an island growth mechanism. X-ray photoelectron spectroscopy (XPS) binding energy shifts for SnP1.00 were 487.2 eV for Sn 3d(5/2) and 133.6 eV for P 2rho(3/2). Energy dispersive X-ray analysis (EDXA) and electron probe studies gave elemental ratios that were in agreement indicating slightly tin rich and stoichiometric films, with negligible chlorine or bromine incorporation (SuP(1.33)-SnP0.40). No Raman scattering was observed. Sheet resistance measurements indicated the films were insulating. Optically the films showed very poor reflectance (approxiinately 2%) and 5-20% total transmissions from 300 to 800 nm. Contact angle measurements were in the range 70-80degrees, and showed little change after 60-min irradiation at 254 nm

Titanium sulfide thin films from the aerosol-assisted chemical vapour deposition of [Ti(SBut)4]

Gold, reflective TiS2 films have been produced from the single-source precursor [Ti(SBut)4] by aerosol-assisted chemical vapour deposition on glass. Films were deposited between 150 and 300 °C using hexanes, dichloromethane or toluene solvent. The titanium sulfide films were analysed by Raman, UV-Vis spectroscopy, scanning electron microscopy (SEM), X-ray powder diffraction, energy dispersive analysis of X-rays (EDAX) and X-ray photoelectron spectroscopy (XPS).

Dual source APCVD synthesis of TaN and NbN thin films on glass from the reaction of MCl5 (M = Ta, Nb) and 1,1,1,3,3,3-hexamethyldisilazane

Niobium nitride films were synthesised by the reaction of niobium pentachloride and hexamethyldisilazane (NH(SiMe3)2, HMDS) under atmospheric pressure chemical vapour deposition (APCVD) conditions. Films were deposited at 400–580 °C in a cold wall CVD reactor. X-ray photoelectron spectroscopy showed that the films consist of niobium and nitrogen with binding energy shifts of 206.8 eV for Nb 3d and 396.8 eV for N 1s. In a similar manner tantalum pentachloride was reacted with HMDS under APCVD at 400–580 °C to give reflective silver films consisting of tantalum nitride. EDAX analysis showed the presence of tantalum and nitrogen in these films. Both sets of films were hard and chemically inert to common solvents and acids, they were also crystalline at substrate temperatures of 550 °C and above showing the typical cubic NaCl pattern of refractory nitrides (TaN a = 4.34(1) A; NbN a = 4.33(1) A). Raman patterns of the films were somewhat indistinct but matched bulk samples. The films were an aesthetically pleasing silver colour and showed no change in optical properties when stored in air for over two years; the films have potential as decorative reflective coatings.

Dual source atmospheric pressure chemical vapour deposition of TiP films on glass using TiCl4 and PH2But

A facile new method for the preparation of large area titanium phosphide films on glass is described from the atmospheric pressure chemical vapour deposition of titanium tetrachloride and tert-butylphosphine.

Chemical vapour deposition of group Vb metal phosphide thin films

The atmospheric pressure chemical vapour deposition (APCVD) reaction of VCl4 or VOCl3 with cyclohexylphosphine at substrate temperatures of 600 °C deposits thin films of amorphous vanadium phosphide. The films are black–gold, hard, chemically resistant and conductive. The APCVD reaction of MCl5 (where M = Nb or Ta) with cyclohexylphosphine at 500–600 °C deposits films of crystalline β-MP and at 400 °C–450 °C amorphous films of stoichiometry MP are formed. The MP films are metallic, conductive, adherent and chemically resistant.

Chemical vapour deposition of crystalline thin films of tantalum phosphide

Tantalum phosphide coatings were prepared by chemical vapour deposition reaction of TaCl5 and PH2Cy at 350-500 degreesC. The films are hard, stable to corrosive environments and show reflection properties in the infrared